The invention relates to a waveguide oscillator with both electrical and mechanical means for altering the operating characteristics of the oscillator.
Such oscillators are widely used in microwave technology. A typical oscillator of this kind comprises mechanical means to provide a coarse adjustment of the operating frequency of the oscillator and a tuning varactor to provide a fine adjustment of the operating frequency and/or for frequency modulation.
Oscillators with both mechanical and electronic tuning are discussed in the paper "Analytic Model for Varactor-Tuned Waveguide Gunn Oscillators" by A. S. Templin and R. L. Gunshor, IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-22, No. 5 (May 1974), pp 554-556. This paper presents the results of calculations (using two different theoretical models) and experimental data for two oscillator configurations each comprising a length of full-height X-band waveguide containing a Gunn diode and a varactor diode spaced along the waveguide from one another and from a movable short-circuit termination at one end of the waveguide; each of the diodes is coupled to the waveguide with a respective mounting post. In one oscillator configuration ("case 1"), the Gunn diode is longitudinally intermediate the varactor diode and the short-circuit, while in the other ("case 2") the converse applies. In each case, the range of electronic tuning obtainable with a change in varactor bias is dependent on the position of the short-circuit. In case 1 (Gunn diode closer than the varactor diode to the short-circuit), wherein the centre frequency of the oscillator is said to be primarily determined by the spacing between the Gunn diode mounting post and the short-circuit, the oscillator has a very wide mechanical tuning range (8.5-12.0 GHz) but the electronic tuning range is critically dependent on the position of the short-circuit and is very small (less than 10 MHz). In case 2 (varactor diode closer than the Gunn diode to the short-circuit), wherein the centre frequency is said to be primarily determined by the spacing between the Gunn device mount and the varactor mounting post, the electronic tuning range varies with the position of the short-circuit in a fairly regular manner from zero up to a somewhat larger maximum value of 50-70 MHz, but the mechanical tuning range is much smaller than in case 1.